The present invention relates to environmental control systems (ECSs), and more particularly to an air cycle subsystem that is in a heat exchange relationship with one or more liquid cycle subsystems.
ECSs provide a supply of conditioned air to an enclosure, such as an aircraft cabin and cockpit. Conventional ECSs have utilized an air-to-air cycle cooling system which is in a heat exchange relationship with a liquid loop. The liquid loop typically cools other heat loads such as avionics packages. Interaction between the air and liquid subsystems is relatively complex. Moreover, air flow sequencing, particularly for multi-turbine ACMs, radically effects ECS efficiency. In many instances much thermal energy is wasted or otherwise inefficiently used.
In one conventional system, a flow of bleed air is taken from an intermediate or high pressure stage within a jet engine. The bleed air is pre-cooled within an air-to-air heat exchanger with heat being rejected to RAM air and then flowed to a compressor of the ACM. After compression, the air is routed through a second air-to-air heat exchanger, a regenerative heat exchanger and an air-to-air reheater heat exchanger. Condensed water vapor is extracted by a water extractor, and dehumidified air is routed to a turbine. Expanded air from the turbine flows through another water collector and into a liquid-to-air heat exchanger of the liquid loop. A relatively warmer liquid in the liquid loop which is used to cool the avionics is thereby cooled. From the liquid-to-air heat exchanger, the air passes through the reheater heat exchanger. The dehumidified air is then passed into a second turbine of the ACM where it is again expanded and passed through another liquid-to-air heat exchanger to further absorb heat from the liquid loop.
Disadvantageously, convention air flow sequences may not effectively reduce heat loads and relatively numerous reheaters and water extractors are required. The water extractors must also extract water from the fog-like water vapor prevalent in conventional ECSs. This may be a relatively difficult and energy inefficient process. Further, the additional components and ducting of the air cycle subsystem increases complexity which may offset the space reductions obtained with the relatively smaller liquid-to-air heat exchangers.
Accordingly, it is desirable to provide an air flow sequence for an ECS which more efficiently utilizes the bleed air as a cooling medium. It is further desirable to recover thermal energy from a liquid cycle subsystem to further increase ACM efficiency.
The environmental control system (ECS) according to the present invention includes an air cycle subsystem that is in a heat exchange relationship with one or more liquid cycle subsystems. Bleed air is typically received from a gas turbine engine or other source and sent through an air-to-air heat exchanger prior to be communicated with an air cycle machine (ACM) having a first and second turbine.
Compressed air exits the compressor of the ACM and is communicated to a reheater and a condenser to further cool the water vapor bearing air by condensing and separating the water into a water extractor. As the water vapor bearing air is passed directly from the reheater to the condenser, the water from the water vapor forms as relatively large droplets which are readily collected by the extractor. Such droplets are comparably easy to separate as compared to fog-like water vapor bearing air.
Dehumidified air exits the extractor and is communicated to an air-liquid heat exchanger of the liquid cycle subsystem. The liquid cycle subsystem reduces the thermal energy from a heat load which is typically an avionics subsystem. Dehumidified heated air exits the first air-liquid heat exchanger and is communicated with the first turbine. The air is expanded through the first turbine of the ACM between the first turbine inlet pressure and the second turbine outlet pressure. Recovered heat from the first air-liquid heat exchanger increases available power of the first turbine.
The discharge pressure from the first turbine is maintained at a discharge temperature just above freezing (mid-pressure) so that the first turbine outlet air operates as a heat sink for the condenser and reheater. The first turbine outlet air recovers further thermal energy from the condenser and the reheater.
Heated air exits the reheater and is communicated with the second turbine. The recovered thermal energy from the condenser and the reheater is used by the second turbine to increase its efficiency. The air is expanded through the second turbine of the ACM and communicated with a second air-liquid heat exchanger to cool a second heat load. Thus, the performance of both turbines is improved from otherwise wasted thermal energy. Moreover, the increases available power advantageously allows the minimization of size and/or weight of the heat exchangers.
The present invention therefore provides an air flow sequence for an ECS which more efficiently utilizes the bleed air as a cooling medium. The present invention also recovers thermal energy from a liquid cycle subsystem to further increase the ACM power output.